Rolling bearing and its packaging method

Abstract

To provide a rolling bearing in which a favorable antirust performance can be obtained while reducing an amount of antirust oil than before, after removing chloride ions and sulfate ions from the entire surface of the bearing, antirust oil is provided to adhere thereto at an average film thickness of 4.5 μm to 10 μm, and the entire bearing is covered with a volatile corrosion inhibitor film such that a space between the volatile corrosion inhibitor film and the bearing is kept in a pressure-reduced condition.

Description

Because the adhered chloride ions effect rusting of the rolling bearing,

Then, each test sample was left in a high temperature and high humidity environment of 50° C.-90% RH and periods of time until rust was occurred were compared. In the environment of 50° C.-90% RH, an effect of accelerating rusting by approximately 30 times is obtained as compared when samples were left at 20° C.-70% RH, which are the average temperature and humidity in Japan, and the equivalent numbers of years are shown in the figure. The results are shown in FIG. 7, but it can be found that, when the adhered amount of antirust oil is less than an average film thickness of 4.5 μm, antirust performance in a packed state is significantly decreased. From the results, it can be found that a favorable antirust performance can be kept for a long time by setting the adhered amount of antirust oil to an average film thickness of 4.5 μm or more.

Test Example 2

Grease Holding Ability Test

The test samples fabricated in Test example 1 were opened and then a bearing interior space defined by an inner ring, an outer ring and balls was charged with grease (MTE produced by NSK Ltd.) of 1.1 g (15% of the bearing interior space volume), thereby fabricating test bearings. Then, after rotating the bearings for 24 hours at conditions as described below, using a tester as shown in FIG. 8, grease residual rates were measured. Also, for comparison, the same bearings, on which cleaning and degreasing was performed and antirust oil was not adhered, were charged with grease to fabricate comparative test bearings, and grease residual rates were in the same manner. The term grease residual rate means a value which is obtained by subtracting a percentage, which is represented by a value obtained by dividing a difference between a bearing weight (M1) in a grease-charged condition before rotating and a bearing weight (M2) after rotating by a charged amount of grease (M3), from 100, and if the grease residual rate is low, a grease life is shortened.

Pre-pressure upon mounting: 120N

Number of revolutions: 10000 min⁻¹ (dm·n=54×10⁴)

Operation position: Vertical

Driving method: Belt driving

Cooling of an outer cylinder: No

The results are shown in FIG. 9, but it can be found that when the average film thickness is up to 10 μm, the test bearings have a grease residual rate of 97% on average as compared with the comparative test bearings having a grease residual rate of 99%, and therefore, the test bearings have a grease holding ability equivalent to those in a conventional using method in which grease charge is performed after cleaning and degreasing bearings. On the other hand, when the average film thickness is 15 μm or more, the grease residual rate tends to be decreased. From the results, it can be found that a grease holding ability equivalent to those in a conventional case, and thus a lubrication lifetime can be kept by setting the adhered amount of antirust oil to an average film thickness of 10 μm or less.

Test Example 3

Grease Precipitation Test

Test bearings prepared by cleaning deep groove ball bearings of a bearing number 6202 with a water substitution type cleaning agent, providing antirust oil to adhere at an average film thickness of 10 μm and then charging with grease (MTE or MTS produced by NSK Ltd., or ISOFLEX NBU 15 produced by NOK KLÜBER Co., Ltd.), and comparative test bearings prepared by cleaning and degreasing, and charging with the grease without providing the antirust oil to adhere, were fabricated, 10 units for each test bearing, 60 units in total.

Also, after each test bearing was placed in a constant temperature bath and then a heating cycle in which the temperature is changed from “0° C.→30° C.→60° C.” every few hours, was repeated 7 times, a noise count measurement was performed one time, and such a measurement was performed 4 times in total. Noise counts before and after heating cycles of bearings were measured using a noise tester mounted in a known anderon device (acoustic measurement device).

The results are shown in FIG. 10, but no significant difference between test bearings and comparative test bearings in initial noise count number and noise count number after heating cycles of 4 times was exhibited. From the results, it can be found that, by setting the adhered amount of antirust oil to an average film thickness of 10 μm or less, precipitation of crystals due to reaction of grease is not occurred.

Test Example 4

Bearing Temperature Rise Test

Test samples, in which the adhered amount of antirust oil in Test example 1 were adjusted to an average film thickness of 10 μm, were opened and then were charged with grease (MTE produced by NSK Ltd.) of 1.1 g (15% of the bearing interior space volume), thereby fabricating test bearings. Also, for comparison, comparative test bearings, which were charged with grease without adhering antirust oil after cleaning and degreasing, were fabricated. Then, each test bearing was rotated at conditions as described below, using the test apparatus used in Test example 2, and a temperature of the outer ring thereof at that time was measured.

Pre-pressure upon mounting: 120N

Number of revolutions: 12000 min⁻(dm·n=65×10⁴)

Operation position: Vertical

Driving method: Belt drive

Cooling of outer cylinder: No

The results are shown in FIG. 11, but no significant difference between test bearings, on which the antirust oil was adhered at the average film thickness of 10 μm, and comparative test bearings in temperature rise characteristics was exhibited. From the results, it can be found that a temperature rise characteristics equivalent to those in a conventional case can be kept by setting the adhered amount of antirust oil to an average film thickness of 10 μm or less.

(Verification of Residual Chloride Ion Amount)

After rolling bearings were fabricated by typical grinding process and all surfaces thereof were ground, chloride ions adhered thereon were removed to become below a detection limit of an analyzer.

After such pretreatment, chloride ions were newly adhered by treatments shown in Table 1, and then an amount of chloride ions was measured. For the measurement, after rolling bearings were immersed in a bath, in which a predetermined amount of ultrapure water was filled, during 2.5 hours at a temperature of 80° C. so that chloride ions were dissolved, a liquid was collected from the bath and then an amount of chloride ions therein were measured by a ion chromatography analyzer, DX-120, and a separation column, IonPacAS12A (4 mm), which are produced by Dionex K.K. The measurement method was performed at conditions identical to those of Explanation FIG. 6 of JIS K0127. Qualification was performed for chloride ions, thereby calculating an amount per unit area. The results are shown in Table 1.

For rolling bearings, on which the same treatment was performed, a rusting acceleration test was performed. In the rusting acceleration test, after the antirust oil was applied to the rolling bearings at an average film thickness of 4.5 μm and the rolling bearings are left for thirty days in a high temperature and high humidity environment of 50° C., 90% RH, whether or not the surfaces of rolling bearings were rusted was verified. The results are shown in Table 1.

TABLE 1
	Bearing surface	Amount of
Samples	treatment method	chloride ions	Rusting
1	Applying chloride ions by hand	13	ng/mm2	Yes
2	Cleaning Sample 1 to remove	5	ng/mm2	No
	chloride ions
3	Applying artificial fingerprint	25	ng/mm2	Yes
	liquid defined by JIS K 2246
4	Cleaning Sample 3 to remove	10	ng/mm2	No
	chloride ions

As shown in Table 1, rusting can be prevented when an amount of chloride ions is 5 ng/mm² to 10 ng/mm².

In addition, assuming that an amount of chloride ions contained in a grinding water is 0.1 mg/L, which is a minimum defined in the Waterworks Law, it is believed that rolling bearings, which are typically ground and from which chloride ions does not removed, have chloride ions of few tens to few hundreds ng/mm² adhered thereon, but when chloride ions are not removed, rusting cannot be prevented if the antirust oil has a thin film thickness of less than 4.5 μm.

From this test, it can be found that, when an amount of chloride ions, which have been adhered on rolling bearings after removing chloride ions therefrom, is set to 0.2 ng/mm² to 10 ng/mm², a favorable antirust performance can be obtained by setting a film thickness of the antirust oil to 4.5 μm or more (4.5 μm to 10 μm) as defined in the prevent invention.

Although the present invention has been described with referenced to the detailed and specific embodiments, it should be apparent to those skilled in the art that numerous changes and modifications can be made without departing the scope and spirit of the present invention.This application is based on Japanese Patent Application No. 2013-115810 filed on May 31, 2013, the entire content of which is incorporated herein by reference.

INDUSTRIAL APPLICABILITY

The present invention is suitable for storing and transporting machine tool bearings (in particular, machine tool spindle bearings).

DESCRIPTION OF REFERENCE SIGNS

• • 1 Angular ball bearing
  • 2 Single-row cylindrical roller bearing
  • 2A Inner ring
  • 2B Cylindrical roller
  • 2C Retainer
  • 2D Outer ring
  • 3 Double-row cylindrical roller bearing
  • 3A Inner ring
  • 3B Cylindrical roller
  • 3C Retainer
  • 3D Outer ring
  • 10 Volatile corrosion inhibitor film
  • 11 Sealing portion

Claims

1. A rolling bearing comprising an inner ring, an outer ring, and a plurality of rolling elements retained between the inner ring and the outer ring by a retainer in a rollable manner,

wherein antirust oil is provided to adhere, at an average film thickness of 4.5 μm to 10 μm, to an entire surface of the bearing from which chloride ions and sulfate ions are removed, the entire bearing is covered with a volatile corrosion inhibitor film, and a space between the volatile corrosion inhibitor film and the bearing is kept in a pressure-reduced condition.

2. The rolling bearing according to claim 1, wherein an amount of residual chloride ions adhered to the rolling bearing per unit area is 0.2 ng/mm² to 10 ng·mm².

3. The rolling bearing according to claim 1, A rolling bearing comprising an inner ring, an outer ring, and a plurality of rolling elements retained between the inner ring and the outer ring by a retainer in a rollable manner,

wherein antirust oil is provided to adhere, at an average film thickness of 4.5 μm to 10 μm, to an entire surface of the bearing from which chloride ions and sulfate ions are removed, the entire bearing is covered with a volatile corrosion inhibitor film, and a space between the volatile corrosion inhibitor film and the bearing is kept in a pressure-reduced condition,

wherein the entire bearing is covered with the volatile corrosion inhibitor film and the space between the volatile corrosion inhibitor film and the bearing is kept in the pressure-reduced condition, in a state in which a bearing interior space defined by the inner ring, the outer ring, and the rolling elements is charged with grease.

4. A method of packaging a rolling bearing after assembling the rolling bearing from bearing components, the method comprising:

after removing chloride ions and sulfate ions from an entire surface of the bearing, providing antirust oil to adhere thereto at an average film thickness of 4.5 μm to 10 μm, and covering the entire bearing with a volatile corrosion inhibitor film such that a space between the volatile corrosion inhibitor film and the bearing is kept in a pressure-reduced condition.

5. The method of packaging the rolling bearing according to claim 4, wherein the chloride ions and the sulfate ion are removed from the entire surface of the rolling bearing such that an amount of residual chloride ions adhered to the rolling bearing per unit area is 0.2 ng/mm² to 10 ng/mm².

6. The method of packaging the rolling bearing according to claim 4, A method of packaging a rolling bearing after assembling the rolling bearing from bearing components, the method comprising:

after removing chloride ions and sulfate ions from an entire surface of the bearing, providing antirust oil to adhere thereto at an average film thickness of 4.5 μm to 10 μm, and covering the entire bearing with a volatile corrosion inhibitor film such that a space between the volatile corrosion inhibitor film and the bearing is kept in a pressure-reduced condition,

wherein after the adhesion of the antitrust oil, a bearing interior space defined by an inner ring, an outer ring and rolling elements is charged with grease, and the entire bearing is covered with the volatile corrosion inhibitor film such that the space between the volatile corrosion inhibitor film and the bearing is kept in the pressure-reduced condition.